Biomass conversion process

ABSTRACT

Biomass is used as a co-feed for a heavy petroleum oil coking process to improve the operation of the coking process and to utilize biomaterial for the production of transportation fuels. The coking process may be a delayed coking process or a fluidized bed coking process and in each case, the presence of the biomass will decrease the coke drying time so reducing coke handling problems in the unit besides forming a superior coke product. In the case of a fluidized bed coking process using a gasifier for the coke, the addition of an alkali metal salt improves the operation of the gasifier.

CROSS REFERENCE TO RELATED APPLICATIONS

This application relates and claims priority to U.S. Provisional PatentApplication No. 61/317,587, filed on Mar. 25, 2010. This application isalso related to U.S. patent application Ser. No. 13/037,938 entitled“Biomass Conversion Process”, filed on Mar. 1, 2011, which claimspriority to U.S. Provisional Patent Application No. 61/317,545 andco-pending U.S. patent application Ser. No. 12/828,405, filed on Jul. 1,2010, which claims priority to U.S. Provisional Patent Application No.61/270,595, filed on Jul. 10, 2009, which relates to the addition ofalkali metal compounds to heavy oil feeds used in delayed cokingprocesses.

FIELD OF THE INVENTION

The present invention relates to a process for the production of liquidtransportation fuels by the conversion of biomass.

BACKGROUND OF THE INVENTION

Petroleum is currently estimated to account for over 35% of the world'stotal commercial primary energy consumption. Coal ranks second with 23%and natural gas third with 21%. The use of liquid hydrocarbon fuels onan enormous scale for transportation has led to the depletion of readilyaccessible petroleum reserves in politically stable regions and this, inturn, has focused attention, economically, technically and politicallyon the development of alternative sources of liquid transportationfuels. Liquid hydrocarbons are far and away the most convenient energysources for transportation in view of their high volumetric energy. Theenergy density of gasoline, for example at about 9 kWh/liter and of roaddiesel at about 11 kWh/liter, far exceeds that of hydrogen (1.32kWh/liter at 680 atm, or batteries, 175 Wh/kg. Furthermore, the liquidhydrocarbon fuel distribution infrastructure is efficient and already inplace.

Production of liquid fuels from biomass can help solve the problem ofCO₂ emission from the transportation sector because CO₂ released fromvehicle exhaust is captured during biomass growth. While direct,carbon-neutral use of biomass as fuel is established, for example,biodiesel, this route is limited because the limited choice of sourcematerials, e.g. vegetable oils. Conversion of a wider variety of biomasssources into more traditional types of fuel, principally hydrocarbons,is the more attractive option.

Currently, there are two major routes for conversion of biomass toliquid fuels: biological and thermo-chemical. In the biological process,fermentation of easily fermentable plant products, such as, for example,sugars to alcohols is achieved. These easily fermentable plant productscan be extracted from corn kernels, sugar cane and etc. The majordisadvantage of this pathway is that only a fraction of the total carbonin biomass is converted to the final desired liquid fuel. It has beencalculated that conversion of all corn produced in USA to ethanol canmeet 12% of entire US demand for gasoline which reduces to 2.4% afteraccounting for fossil fuel input required to produce the ethanol.

One well-established route to the production of hydrocarbon liquids isthe gasification of carbonaceous materials followed by the conversion ofthe produced synthesis gas to form liquids by processes such asFischer-Tropsch and its variants. In this way, solid fuels such as coaland coke may be converted to liquids. Coal gasification iswell-established, being used in many electric power plants and the basicprocess can proceed from just about any organic material, includingbiomass as well as waste materials such as paper, plastic and usedrubber tires. Most importantly, in a time of unpredictable variations inthe prices of electricity and fuels, gasification systems can provide acapability to operate on low-cost, widely-available coal reserves.Gasification may be one of the best ways to produce clean liquid fuelsand chemical intermediates from coal as well as clean-burning hydrogenwhich also can be used to fuel power-generating turbines or used in themanufacture of a wide range of commercial products. Gasification iscapable of operating on a wide variety of input materials, can be usedto produce a wider variety of output fuels, and is an extremelyefficient method of extracting energy from biomass. Biomass gasificationis therefore technically and economically attractive as an energy sourcefor a carbon constrained economy.

The conversion of biomass to hydrocarbon transportation fuels by thegasification-liquefaction sequence has, however, certain limitationsboth technically and economically. First, the conversion of the biomassto synthesis gas requires large process units, high in capital cost todeal with the enormous volumes of gas generated in the process. Second,the gas-to-liquid conversion uses catalysts which may, for optimumresults, use noble metal components and accordingly be very expensive.Third, and by no means least is the fact that enormous biologicalresources are needed to supply current consumption levels. Anapproximate estimate for the land area required to support the currentoil consumption of about 2 million cubic meters per day by the UStransportation sector is of the order of 2.67 million square km whichrepresents 29% of the total US land area, using reasonable assumptionsfor the efficiency of the conversion process, thus suggesting that largescale production of liquid fuels from such a biomass conversion processis impractical.

SUMMARY OF THE INVENTION

We have now found that biomass may be effectively converted into liquidtransportation fuels and other products by the well-establishedpetroleum refinery coking processes of delayed coking and fluidized bedcoking. While the limited availability of biomass and the oils derivedfrom biomass precludes the process from addressing any large proportionof total transport energy needs, it does provide a route for usingavailable resources efficiently and economically.

According to the present invention, biomass is used as a co-feed for aheavy petroleum oil coking process to improve the operation of thecoking process and to utilize the biomaterial for the production oftransportation fuels. The coking process may be a delayed coking processor a fluidized bed coking process and in each case, the presence of thebiomass will decrease the coke drying time while reducing coke handlingproblems in the unit. In the case of a fluidized bed coking processusing a gasifier for the coke such as in the Flexicoking™ process, theaddition of an alkali metal salt improves the operation of the gasifieras described below.

The present invention can therefore be seen to provide a twofoldimprovement. According to one aspect, the operation of a heavy petroleumoil feed is used in a coking process is improved by the use of thebiomass co-feed even in minor amounts. The presence of the bio co-feedto the coker has, besides other benefits, the potential to improve thecoke drying rate by the generation of free radicals from the lignin andthe lignin pyroiysis products in the biomass. By improving the dryingrate, fouling of the stripper section is reduced, the coke product iseasier to handle and unit capacity (throughput) can be increased ascycle time decreases.

In its first aspect, therefore, the present invention provides a methodof improving the operation of a heavy petroleum oil coking process inwhich a heavy petroleum oil feed is heated to an elevated temperature atwhich the feed is subject to coking; the improvement comprisesco-feeding biomass with the heavy petroleum oil feed into the coker. Thecoking process may be either a delayed coking process or a fluidized bedcoking process such as fluid coking or Flexicoking™.

From another aspect, the use of the biomass in this way improvesutilization of biological materials and reduces the demand for fossilfuels, especially petroleum. In this, its second aspect, the presentinvention provides a process for the conversion of biomass into liquidtransportation fuel and fuel precursor components by blending thebiomass with a heavy petroleum oil to form a feed stream for a cokingprocess.

There are significant synergies for the conversion of the biomass in thecoker which include steam conversion of oxygenated species, thermalconversion and coke disposal. These synergies, by using a coker,dramatically increase the efficiency of thermal biomass conversionoperations which produce coke, tars and hydrocarbon insoluble oils.

DETAILED DESCRIPTION

Biomass is conventionally defined as the living and recently deadbiological material that can be converted for use as fuel or forindustrial production. The criterion as biomass is that the materialshould be recently participating in the carbon cycle so that the releaseof carbon in the combustion process results in no net increase averagedover a reasonably short period of time (for this reason, fossil fuelssuch as peat, lignite and coal are not considered biomass by thisdefinition as they contain carbon that has not participated in thecarbon cycle for a long time so that their combustion results in a netincrease in atmospheric carbon dioxide). Most commonly, biomass refersto plant matter grown for use as biofuel, but it also includes plant oranimal matter used for production of fibers, chemicals or heat. Biomassmay also include biodegradable wastes that can be burnt as fuelincluding municipal wastes, green waste (the biodegradable wastecomprised of garden or park waste such as grass or flower cuttings andhedge trimmings), byproducts of farming including animal manures, foodprocessing wastes, sewage sludge, black liquor from wood pulp or algae.It excludes organic material which has been transformed by geologicalprocesses into substances such as coal, oil shale or petroleum. Biomassis widely and typically grown from plants, including miscanthus, spurge,sunflower, switchgrass, hemp, corn (maize), poplar, willow and othertrees, sugarcane, and oil palm (palm oil) with the roots, stems, leaves,seed husks and fruits all being potentially useful. The particular plantor other biomass source used is not important to the product liquidtransportation fuel although the processing of the raw material forintroduction to the processing unit will vary according to the needs ofthe unit and the form of the biomass.

In the present process, the biomass after any necessary or desiredcomminution and/or drying to improve handling and mixing with the heavyoil stream, is fed into a refinery coking process along with a heavypetroleum oil feed.

The petroleum coking process is well-established in refinery operation.There are three main variants of the coking process: delayed coking,fluid coking and its variant, the Flexicoking™ process. Delayed cokingis the variant with the greatest global installed capacity while fluidcoking processes (the term is used to include contact coking andFlexicoking) are becoming of greater interest with the need to maximizeefficiency and utilize resources as efficiently as possible. The movingbed continuous contact coking process now appears to be obsolete.

In delayed coking, a heavy oil feed is heated in a continuouslyoperating process furnace to effect a limited extent of thermalcracking, after which it enters a large, vertically-oriented cylindricalvessel or coking drum, in which the coking reactions take place. Theterm “delayed” coker refers to the fact that the coking reactions do nottake place in the furnace, but rather are delayed until the oil entersthe coke drum. In the coke drum, large oil molecules are furtherthermally cracked to form additional lighter products and residual coke,which fills the vessel. The lighter hydrocarbons flow out of the drum asvapor and are further processed into fuel products. Gradually the cokeaccumulates in the drum until it is almost filled with coke. When thedrum is nearly filled, the hot oil from the furnace is directed to aclean coke drum, while the full one is decoked. The decoking cycleinvolves cooling and depressuring the drum, purging it with steam toremove residual hydrocarbon vapor, opening up the top and bottom heads(closures) on the drum and then using high pressure water lances ormechanical cutters to remove the coke from the drum. The coke falls outthe bottom of the drum into a pit, where the water is drained off andconveyers take the coke to storage or rail cars. The drum is then closedup and is ready for another coking cycle. The many descriptions of thedelayed coking process are too numerous to detail but useful summariesmay be found in “Kirk Othmer Encyclopedia of Chemical Technology”, vol.17, John Wiley & Sons, New York, 1982, ISBN 0-471-02070-2, pp. 210-215;“Modern Petroleum Technology”, Hobson (Ed.), Applied Science Publ.,Barking, 1973, ISBN 085334-487-6, pp. 283-288; “Petroleum Refining,Technology and Economics”, Gary and Handwerk, Marcel Dekker, NY 1994,ISBN 0-8247-9157-6 page 71; “SYDEC” Selective Yield Delayed Coking,publication of Foster Wheeler, N.J., 1995; “Tutorial: Delayed CokingFundamentals”, Ellis et al, Great Lakes Carbon Corporation, Port Arthur,Tex., prepared for presentation at the AIChE 1998 Spring NationalMeeting, New Orleans, La., Mar. 8-12, 1998, available online athttp://www.coking.com/DECOKTUT.pdf.

A number of recent proposals have been made for increasing the capacityof delayed cokers by intentionally producing a free-flowing shot cokeproduct; in this way, the significant proportion of coker cycle timetaken in the draining and cutting operations can be eliminated so thatshorter cycle times and greater throughput are achieved. These proposalsmay be found, for example, in U.S. Pat. Nos. 7,303,644; 7,306,713;7,374,665, 7,645,375, 7,727,382 and 7,658,838 and in U.S. PublicationNos. US 2005/0279673 and US 2006/0060506.

Fluidized bed coking is a petroleum refining process in which heavypetroleum feeds, typically the non-distillable residue (resid) fromfractionation, are converted to lighter, more useful products by thermaldecomposition (coking) at elevated reaction temperatures, typicallyabout 480 to 590° C., (about 900 to 1100° F.). The process is carriedout in a unit with a large reactor vessel containing hot coke particleswhich are maintained in the fluidized condition at the required reactiontemperature with steam injected at the bottom of the vessel with theaverage direction of movement of the coke particles being downwardsthrough the bed. The heavy oil feed is heated to a pumpable temperature,mixed with atomizing steam, and fed through multiple feed nozzlesarranged at several successive levels in the reactor. The steam isinjected into a stripper section at the bottom of the reactor and passesupwards through the coke particles in the stripper as they descend fromthe main part of the reactor above. A part of the feed liquid coats thecoke particles in the fluidized bed and subsequently decomposes intolayers of solid coke and lighter products which evolve as gas orvaporized liquid. The light hydrocarbon products of the coking (thermalcracking) reactions vaporize, mix with the fluidizing steam and passupwardly through the fluidized bed into a dilute phase zone above thedense fluidized bed of coke particles. This mixture of vaporizedhydrocarbon products formed in the coking reactions continues to flowupwardly through the dilute phase with the steam at superficialvelocities of about 1 to 2 meters per second (about 3 to 6 feet persecond), entraining some fine solid particles of coke. Most of theentrained solids are separated from the gas phase by centrifugal forcein one or more cyclone separators, and are returned to the densefluidized bed by gravity through the cyclone diplegs. The mixture ofsteam and hydrocarbon vapor from the reactor is subsequently dischargedfrom the cyclone gas outlets into a scrubber section in a plenum locatedabove the reaction section. The heavy fraction separated in the scrubberis typically recycled to extinction by feeding back to the fluidized bedreaction zone while the lighter cracking products pass on to the productrecovery section.

The Flexicoking™ process, developed by Exxon Research and EngineeringCompany, is, in fact, a fluidized bed coking process that is operated ina unit including a reactor and burner, often referred to as a heater inthis variant of the process, as described above but also including agasifier for gasifying the coke product by reaction with an air/steammixture to form a low heating value fuel gas. The heater, in this case,is operated with an oxygen depleted environment. The gasifier productgas, containing entrained coke particles, is returned to the heater toprovide a portion of the reactor heat requirement. A return stream ofcoke sent from the gasifier to the heater provides the remainder of theheat requirement. Hot coke gas leaving the heater is used to generatehigh-pressure steam before being processed for cleanup. The coke productis continuously removed from the reactor. In view of the similaritybetween the Flexicoking process and the fluid coking process, the terms“fluidized bed coking” and “fluid coking” are used in this specificationto refer to and comprehend both fluid coking and Flexicoking except whena differentiation is required.

Both the fluid coking process and the Flexicoking process are wellknown. See, for example, “Petroleum Processing” Hengestebeck,McGraw-Hill, NY 1959, pp. 138-139; “Petroleum Processing Handbook”,Bland and Davidson, McGraw-Hill, NY 1967, pp. 3-68-69; “Modern PetroleumTechnology”, ibid.; “Kirk Othmer Encyclopedia of Chemical Technology”,ibid.

The petroleum feedstocks generally used in coking units are typicallythe heaviest (highest boiling) fractions of crude oil that are separatedin the crude fractionation unit, normally comprising an atmosphericdistillation tower and vacuum tower. The nature of the coke formed ishighly dependent on the characteristics of the feedstock to the coker aswell as upon the operating conditions used in the coker. Generally, thedelayed coker is considered to produce three types of coke that havedifferent values, appearances and properties. Needle coke, sponge coke,and shot coke are the most common. Needle coke is the highest quality ofthe three varieties which commands a premium price; upon further thermaltreatment, needle coke which has high electrical conductivity (and a lowcoefficient of thermal expansion) is used to make the electrodes inelectric arc steel production. It is low in sulfur and metals and isfrequently produced from some of the higher quality coker feedstocksthat include more aromatic feedstocks such as slurry and decant oilsfrom catalytic crackers and thermal cracking tars. Typically, it is notformed by coking of resid type feeds. Sponge coke, a lower quality coke,is most often formed in refineries from lower quality refinery cokerfeedstocks having significant amounts of asphaltenes, heteroatoms andmetals. If the sulfur and metals content is low enough, sponge coke canbe used for the manufacture of anodes for the aluminum industry. If thesulfur and metals content is too high for this purpose, the coke can beused as fuel. Shot coke is considered the lowest quality coke. The term“shot coke” comes from its spherical or ovoidal shape ball-like shape,typically in the range of about 1 to about 10 mm diameter. There is alsoanother coke, which is referred to as “transition coke” and refers to acoke having a morphology between that of sponge coke and shot coke. Thefluidized bed coking processes produce a different type of coke formedof small fairly dense particles, often with an internal layeredstructure arising from the process of formation. Control of particlesize in fluid coking is effected by the use of attrition steam injectedinto the lower portion of the reactor at supersonic velocity.

In the present process, the biomass is used as a co-feed with the heavypetroleum oil feed to the coking unit which may be a delayed coker or afluidized bed coker. The biomass is not generally hydrocarbon soluble,but can be dispersed into many heavy oils of the type used as cokerfeeds. While the resins and asphaltenes in asphaltic resids are morepolar and would provide increased solvency for the polar species inbiomass and their pyrolysis products, the increased degree of solvencyof the biomass itself is likely to be fleeting because of the hightemperatures involved causing depolymerization. The biomass may beshredded or ground into a suitable form for handling, e.g. by a hammermill and then injected into a stream of the heavy oil pre-heated to atemperature adequate to make it pumpable. Screw feeders having a portopening into the feed stream line are suitable for injecting thebiomass.

Vacuum resids form the major proportion of heavy oil coker feeds, e.g.vac resids from crudes such as Off-shore Marlim, Bachaquero,Lloydminster/Wainwright, Maya, Cold Lake; Louisiana Sweet; HeavyCanadian; Campana. Atmospheric (long) resids may also be used as well asvisbreaker bottoms, aromatic extracts, slurry oils and other heavyfractions.

The conventional practice in delayed coking is to inject steam into thefurnace mainly to assist in increasing the velocity in the furnace tubesespecially in the event that oil flow is momentarily is lost ordecreased so as to reduce the likelihood of coking up the furnace tubes;the added steam also reduces the partial pressure of the oil in the drumso that more gas oil product is carried out of the drum. Velocity steamis typically added at around 1 wt % of the feed. Vaporization of thewater content of the added biomass plus the water generated bydehydration reactions, especially from cellulose, will normally beplentiful and will generate more steam and, together with the velocitysteam, is likely to lead to reactions such as rapid hydrolysis,cleavage, decarbonylation and decarboxylation of the biomass oil at thetemperatures encountered in the coking process, typically about 500° C.in a delayed coker furnace or transfer line to the coke drum. In afluidized bed coking process, the pre-heat in the scrubber section atabout 345° C. prior to entry into the reactor at about 530° C. willachieve the same result. Hydroxyaromatics such as phenols and naphtholswould survive this hydrothermal exposure but these would be diluted intothe coker liquids generated from the resid portion of the feed and couldbe deoxygenated as part of the more dilute total product streams duringdownstream hydrotreatment, or alternatively could be extracted asphenolate salts (water soluble/hydrocarbon insoluble) using a causticextraction process e.g. a Dualayer process with a concentrated potassiumor sodium hydroxide solution containing solubilizer extracts. Anothersuitable extraction process is the process using an aqueous extractantand a contactor which utilizes capillary and surface tension effects tocontact the hydrocarbon phase with a lean treating solution phase in anefficient, non-dispersive manner which improves separation of the twophases. A process of this type is the Exomer^(SM) process available fromMerichem Chemicals and Refinery Services LLC. Mercaptans and residualcarboxylic acids are also removed during this extraction step. Volatilecleaved products largely escape for recovery overhead as hydrocarbonliquids.

One of the principal advantages of co-feeding biomass to a cokingprocess is that the lignin from the biomass generally forms free radicalinitiators at a low activation energy and these initiators decrease thecoke drying time in the coking process, regardless of whether it is adelayed coking process or a fluidized bed process. When the heavypetroleum oil feed is exposed to temperatures of 425-530° C. or higheras it is in the delayed coker furnace, coker drum or the fluid cokingreactor, essentially all the longer alkyl chains on aromatic rings willbe completely cleaved to form methyl aromatics and olefins. This is avery rapid, step with a low activation energy (E_(a)=52 Kcal/mol) and iscomplete in about 50 seconds at 525° C. Additional time is required forthe subsequent step involving the removal of methyl groups remaining onthe aromatic nuclei to form unsubstituted aromatic structures in adry-coke-like material. This step, referred to as “sticky layer coking”requires ˜58-66 Kcal/mole (log A˜14) and would be normally be completedafter a longer residence time in a delayed coker drum or after anextended residence time (average) in the bed of a fluidized process. Ineither case, failure to generate a dry coke is the direct cause ofdifficulty in handling the coke: in the delayed coker, the sticky cokewill agglomerate into a mass as in sponge coke which requirestime-consuming cutting operation to remove it from the drum. If a dryshot coke can be quickly produced, as in the shot coke productionmethods mentioned above, the drum may be drained quickly with aconsequent reduction in cycle time. In fluidized bed coking, a failureto generate a dry, particulate coke during the residence in the bed willlead to fouling problems in the stripper at the base of the reactor andalso in the cyclones and the scrubber section, often leading to frequentand undesirable unit shutdowns. The generation of the free radicals fromthe biomass, however, takes place readily and assists in the rapidhydrogen transfer to aromatic structures and the formation of a dry cokeproduct. As the generation of the free radicals is related to thepresence of the lignins in the charge, a high lignin content ispreferred: lignin contents of at least 35 percent or at least 50 percentlignin would be preferred, if feasible. Unit capacity is increased fromthe abbreviated reaction time and product quality improved and there isalso a potential for decreasing gas make. Cellulosic materials in thebiomass would largely be converted to form coke, which is compatiblewith the coking operations, and water.

Since the biomass will normally be introduced into the coker feed streamin a minor quantity, less than 50 percent of the total feed, cokingshould be carried out at normal temperatures and pressures. In a delayedcoker, the heavy oil feed, e.g. vacuum resid will be pumped to thefurnace at a pressure of about and preferably 300 to 4000 kPa (about 44to 580 psig), where it is heated to a temperature from about 480° C. toabout 520° C. It is then discharged into the coker drum where a lowerpressure prevails to allow volatiles to be removed overhead, typicallyfrom 100 to 400 kPa (about 15 to 58 psig) and preferably in the range of100 to 300 kPa (about 15 to 44 psig). Typical operating temperatures ofthe drum will be between about 410° C. and 475° C. In a fluidized bedunit such as a fluid coker or a Flexicoker, the feed will typically beheated to a temperature at which it is pumpable before passing throughthe scrubber section to pick up heat from the cracked vapors. Thepre-heated feed is then brought to coking temperatures typically in therange of 480 to 565° C. with reactor pressures being almost atmosphericin order to facilitate removal of hydrocarbon volatiles and coke drying.

The conventional practice in delayed coking is to inject steam into thefurnace mainly to assist in increasing the velocity in the furnace tubesespecially in the event that oil flow is momentarily is lost ordecreased so as to reduce the likelihood of coking up the furnace tubes:the added steam also reduces the partial pressure of the oil in the drumso that more gas oil product is carried out of the drum. Velocity steamis typically added at around 1 wt % of the feed. Vaporization of thewater content of the added biomass plus the water generated bydehydration reactions, especially from cellulose, will normally beplentiful and will generate more steam and, together with the velocitysteam, is likely to lead to reactions such as rapid hydrolysis,cleavage, decarbonylation and decarboxylation of the biomass at thetemperatures encountered in the coking process, typically about 500° C.in a delayed coker furnace or transfer line to the coke drum. In afluidized bed coking process, the pre-heat in the scrubber section atabout 345° C. prior to entry into the reactor at about 530° C. willachieve the same result. Hydroxyaromatics such as phenols and naphtholswould survive this hydrothermal exposure but these would be diluted intothe coker liquids generated from the resid portion of the feed and couldbe deoxygenated as part of the more dilute total product streams duringdownstream hydrotreatment, or alternatively could be extracted asphenolate salts (water soluble/hydrocarbon insoluble) using a causticextraction process e.g. Dualayer process with a concentrated potassiumor sodium hydroxide solution containing solubilizer extracts. Anothersuitable extraction process is the process using an aqueous extractantand a contactor which utilizes capillary and surface tension effects tocontact the hydrocarbon phase with a lean treating solution phase in anefficient, non-dispersive manner which improves separation of the twophases. A process of this type is the Exomer^(SM) process available fromMerichem Chemicals and Refinery Services LLC. Mercaptans and residualcarboxylic acids are also removed during this extraction step. Volatilecleaved products largely escape for recovery overhead as hydrocarbonliquids.

As mentioned above, the biomass will normally constitute a minorproportion of the coker feed and in most case will not exceed about 20percent of the total feed, more typically 10 percent. In delayed cokingthe biomass may be blended in with the petroleum oil feed componentupstream or immediately downstream of the combination tower or,alternatively, into the transfer line between the furnace and the cokedrum, which is preferred. In fluidized bed coking, the biomass may beadded directly to the feed line to the scrubber section of the reactorin which it is pre-heated prior to entry into the reactor itself.

When the biomass is used as a co-feed in the Flexicoker process whereportion of the coke product is gasified to provide process heat and fuelgas, it is advantageous to include an alkali metal compound in the feed.This compound becomes incorporated in the coke particles in the reactorand when this coke is sent to the gasifier, promotes the gasification inthe manner described in U.S. Pat. No. 3,689,240 (Aldridge). Thepreferred alkali metal compounds are the salts of which potassiumcarbonate K₂CO₃ and cesium carbonate Cs₂CO₃ are preferred. A mixture oftwo or more compounds may be used. Alkali metal salts such as thesodium, lithium, rubidium salts may be used either alone or incombination with one another and the preferred alkali metal salt anionsinclude, for example, carbonates, acetates, formates. Oxides andhydroxides of alkali metals may also be used. Preferred catalyst saltcompositions would include mixtures of K₂CO₃ and KCl, Cs₂CO₃ and CsCl,K₂CO₃ and Li₂CO₃ or Cs₄CO₃ and Li₂CO₃, although any catalytically-activemixture of alkali metal salt compounds which are stable under reactionconditions may be used. The salts(s) may be supported on an inert base,such as alpha or gamma alumina, silica, zirconia, magnesia, mullite orsupported by a synthetically prepared or naturally occurring material,such as pumice, clay, kieselguhr, diatomaceous earth or bauxite. Themost preferred supported catalysts would be either K₂CO₃ or Cs₂CO₃supported on an alumina base.

Broad Preferred More Preferred Steam to air rate, 0.05-1.0  0.1-0.50.1-0.4 molar ratio basis Temperature, C.  700-1200  800-1100  850-1000Pressure, kPa   0-1000  50-700  50-350The pressures indicated in the above table are indicative of thepressures associated with the FLEXICOKING process. The pressuresassociated with partial oxidation or PDX operations are typicallyhigher.

Another advantage of using the alkali metal compound in delayed cokingis that the addition of the compound(s) to feeds containing very heavyoils such as those from tar sands and the Orinoco Heavy Oil Belt whichwould normally produce a dense coke product which is difficult to removefrom the drum and which is likely to inflame in the coke pit whendischarged. The coke product resulting from the use of alkali metalcompound additive is notable for its lower density and higher porosityrelative to the dense coke product which would be obtained in theabsence of the additive; moreover, it is more friable and usually is incompact, granular form permitting it to be discharged from the drumwithout difficulty. The lower density coke is more amenable to uniformquenching in the drum and so can be cut and discharged with a reducedrisk of eruptions and a reduced risk of fires in the coke pit or whenthe coke is subsequently handled and transported. The improvementprovided by the addition of alkali metal compounds to such heavy oilfeeds is described in co-pending U.S. patent application Ser. No.12/828,405, filed on Jul. 1, 2010, which claims priority to U.S.Provisional Patent Application No. 61/270,595, filed on Jul. 10, 2009,to which reference is made for details of the preferred alkali metalcompounds and their manner of use in delayed coking with heavy oilfeeds.

Heavy oil feeds which may benefit from the addition of the alkali metalcompound during the coking include the highly asphaltic oils such asthose from tar sands, tar pits and pitch lakes of Canada (Athabasca,Alta.), Trinidad, Southern California (La Brea (Los Angeles), McKittrick(Bakersfield, Calif.), Carpinteria (Santa Barbara County, California),Lake Bermudez (Venezuela) and similar deposits in Texas, Peru, Iran,Russia and Poland, may provide similar balances of properties. Crudeoils from the tar sand belt in Venezuela, especially the Orinoco TarBelt and the Cerro Negro part of the Belt are generally characterized bya low API gravity (low hydrogen content), typically in the range of5-20° API and in many cases from 6 to 15° with some ranging from 8 to12° API. Examples include the 8.5° API Cerro Negro Bitumen and crudesfrom the Morichal (8-8.5° API), Jobo (8-9° API), Pilon (13° API) andTemblador (19° API) oilfields. These extra-heavy oils are normallyproduced by conventional enhanced recovery methods including alternatedsteam soaking. The heaviest types of these oils such as the Morichal andJobo crudes are normally diluted at the well-head with gasoil or lightercrudes or processed petroleum fractions such as heavy naphthas,distillates or thermal cracking products including coker gas oils andcoker naphthas, in order to reduce their high viscosity and facilitatetheir transport by pipeline and to attain their sale specification assynthetic crudes, for instance, as the commercial blend known as theMorichal Segregatio (12.5° API) or the blend of Pilon and Temblador soldas Pilon Segregation (13.5° API) or the Pilon blend in which all thecrudes produced from the region are diluted to 17° API with lightercrudes from the adjacent San Tome area.

The invention claimed is:
 1. A method of improving the operation andthroughput of a heavy petroleum oil fluidized bed coking process inwhich a heavy petroleum oil feed is heated to an elevated temperature atwhich the feed is subject to coking, the improvement comprisingco-feeding a biomass comprising lignins and lignocelluloses with theheavy petroleum oil feed into the fluidized bed reactor of the coker todecrease the drying time of the coke product in the reactor by thegeneration of free radicals from lignin and lignocellulose in thebiomass, wherein the biomass comprises at least 35 weight percentlignins.
 2. A method according to claim 1 in which the biomass comprisesplant matter, biodegradable wastes, byproducts of farming, foodprocessing wastes, sewage sludge, black liquor from wood pulp or algae.3. A method according to claim 2 in which the biomass comprises theroots, stems, leaves, seed husks and fruits of miscanthus, spurge,sunflower, switchgrass, hemp, corn (maize), poplar, willow, sugarcane,and oil palm (palm oil).
 4. A method according to claim 1 in which thecoking process is a fluidized bed coking process in which the feedstream is discharged into a fluidized bed coking reactor at a pressurefrom atmospheric to 400 kPa and a temperature of 480 to 565° C.
 5. Amethod according to claim 1 in which the biomass comprises up to 20weight percent of the total feed to the coking process.
 6. A methodaccording to claim 1 in which the biomass comprises up to 10 weightpercent of the total feed to the coking process.
 7. A process for theconversion of a biomass comprising lignins and lignocelluloses intoliquid transportation fuels which comprises: (i) mixing the biomass witha heavy petroleum oil to form a feed stream, wherein the biomasscomprises at least 35 weight percent lignins, (ii) heating the feedstream to an elevated temperature at which the feed stream is subject tocoking and coking the feed stream in a fluidized bed coking reactor toform a coke product with a decrease the drying time of the coke productin the reactor by the generation of free radicals from lignin andlignocellulose in the biomass to increase the throughput of the process.8. A process according to claim 7 in which the biomass comprises plantmatter.
 9. A process according to claim 8 in which the biomass comprisesthe roots, stems, leaves, seed husks and fruits of miscanthus, spurge,sunflower, switchgrass, hemp, corn (maize), poplar, willow, sugarcane,and oil palm (palm oil).
 10. A process according to claim 7 in which thecoking process is a fluidized bed coking process in which the feedstream is discharged into a fluidized bed coking reactor at a pressureof 100 to 400 kPa and a temperature of 480 to 565° C.
 11. A processaccording to claim 7 in which the coking process is a fluidized bedcoking process in which an alkali metal salt is added to the feedstream.